But a rather unusual crew of experienced hikers, skiers, and bikers decided that this week, of all weeks, would be an excellent time to endure a 135-mile ultramarathon.

Starting out near the Canadian border on Monday, the endurance athletes pedaled, walked, ran, and skied the hilly trail between two towns that consistently record some of the coldest temperatures in the nation: International Falls and Tower, Minnesota.

This is the Arrowhead 135, an annual torture test of low temperatures that some people relish.

"They like the challenge," race volunteer Russ Loucks told Business Insider. "There's a good contingent of winter enthusiasts up here who just like doing things in the winter."

The race started at 7 a.m. Monday and followed a groomed snowmobile trail through the woods. Loucks said it was so cold the weekend before the race (temperatures reached -46 Fahrenheit) that the snow was like "packed concrete."

The race started at 7 a.m. Monday and followed a groomed snowmobile trail through the woods. Loucks said it was so cold the weekend before the race (temperatures reached -46 Fahrenheit) that the snow was like "packed concrete."

"It was really fast," Loucks said. So fast that biker Jordan Wakeley set a new speed record: He crossed the finish line 11 hours and 43 minutes after he started. "Jordan's just an animal," Loucks added. "It's not the first time he's won the race."

"It was really fast," Loucks said. So fast that biker Jordan Wakeley set a new speed record: He crossed the finish line 11 hours and 43 minutes after he started. "Jordan's just an animal," Loucks added. "It's not the first time he's won the race."

The race organizers make sure that everyone brings some survival equipment: a sleeping bag, stove, fuel, and food. "Fortunately most of the course is in woods," Loucks said. "But there are some open stretches, and that just really saps people's energy. That's why we require a good a windbreaker."

The race organizers make sure that everyone brings some survival equipment: a sleeping bag, stove, fuel, and food. "Fortunately most of the course is in woods," Loucks said. "But there are some open stretches, and that just really saps people's energy. That's why we require a good a windbreaker."

Temperatures were sub-zero, but the wind was the kicker. Wind chills plunged to -55 Fahrenheit. People protected themselves from the vortex-level temperatures with lots of layers, mittens, and oversized boots with room for multiple socks.

Temperatures were sub-zero, but the wind was the kicker. Wind chills plunged to -55 Fahrenheit. People protected themselves from the vortex-level temperatures with lots of layers, mittens, and oversized boots with room for multiple socks.

A growing body of research suggests some exposure to cold temperatures may be good for us, since that might increase beneficial brown fat stores that help keep us warm and burn calories. (This race is a little extreme, though.)

A growing body of research suggests some exposure to cold temperatures may be good for us, since that might increase beneficial brown fat stores that help keep us warm and burn calories. (This race is a little extreme, though.)

Of the 146 people who started the race, 52 finished.

Of the 146 people who started the race, 52 finished.

“I did get on the edge of hypothermia at the end, but it always amazes me how much heat your body produces," racer Don Gabrielson told Runners World. He finished the race in 21 hours and 23 minutes, riding a fat tire bike. "Unless you stop. You can’t stop, or at least not stop for long."

“I did get on the edge of hypothermia at the end, but it always amazes me how much heat your body produces," racer Don Gabrielson told Runners World. He finished the race in 21 hours and 23 minutes, riding a fat tire bike. "Unless you stop. You can’t stop, or at least not stop for long."

None of the skiers made it all the way this year. The extreme cold is probably to blame for that.

None of the skiers made it all the way this year. The extreme cold is probably to blame for that.

"When the snow gets very cold, the skis do not glide at all. The skiers say it's like Velcro," Loucks said. "You're really struggling with the equipment, and it's just not gliding at all."

"When the snow gets very cold, the skis do not glide at all. The skiers say it's like Velcro," Loucks said. "You're really struggling with the equipment, and it's just not gliding at all."

The last person to cross the finish line arrived more than two days after he started, around 4 p.m. on Wednesday. He completed the course in 56 hours and 58 minutes.

The last person to cross the finish line arrived more than two days after he started, around 4 p.m. on Wednesday. He completed the course in 56 hours and 58 minutes.

Loucks said no one has ever died doing the Arrowhead 135. You have to qualify for it, and race organizers make sure everyone has appropriate survival gear. Unfortunately, elsewhere across the Midwest, at least 21 people died because of the weather this week, a sobering reminder that extreme cold should not be taken lightly.

Loucks said no one has ever died doing the Arrowhead 135. You have to qualify for it, and race organizers make sure everyone has appropriate survival gear. Unfortunately, elsewhere across the Midwest, at least 21 people died because of the weather this week, a sobering reminder that extreme cold should not be taken lightly.